Many researchers have studied the effects of parental alcohol and drug use on child outcomes. These studies conclude that parental substance use has the potential to negatively impact children's psychosocial development by depriving them of adequate care and supervision, impeding their socioemotional and cognitive development and/or influencing them to become substance users as well. Considering a bidirectional, systemic model for understanding the development, maintenance and recovery of substance use problems, it follows that the child impacts parents' behaviors as well. Family therapy has consistently shown that involvement of family members in the treatment of substance users is associated with higher levels of engagement and retention in treatment. Many studies report pre to post treatment reductions in substance use and related problems among those receiving couples and family therapy. While randomized clinical trials of family therapy have involved adult identified patients (IPs) in couples therapy and adolescent IPs in family therapy, this study will evaluate a family systems intervention involving an adolescent child in the treatment plan of the adult treatment seeker. In the current study, alcohol and drug treatment seeking adult mothers of an adolescent child (11-15) living in the home will be engaged. All clients will be randomized to (1) ecologically-based family therapy (EBFT) in the home + treatment as usual (TAU), (2) EBFT at the office + TAU, or (3) TAU + attention control. The relative efficacy of this approach will be evaluated at 3, 6, 12, and 18 months post-baseline. Proposed change mechanisms (mediators) for family therapy will be evaluated. Differential treatment response as a function of gender, family history of alcohol or drug use, and primary alcohol v. drug abuse (moderators) will be investigated to better understand the intervention. The study will also examine how, if at all, treatment engagement and retention impact parent and adolescent response to treatment. Information gained through this project will help evaluate the utility of including adolescent family members in the treatment plan of their adult parents. Finally, the study will include an economic evaluation component to estimate the economic cost of each intervention and determine which condition is most cost effective. Intervention that includes a focus on parent-child interaction has the potential to enhance substance use reductions, reduce parent relapse, and improve family and emotional health among adults. Involvement of the adolescent offers the opportunity to increase the potential protection of a positive parent-child relationship which is shown to be associated with positive developmental outcomes. Narrative Given the reciprocal nature of parent-child interaction, involvement of the adolescent in their mother's substance abuse treatment plan might be associated with reductions in adult relapse and improvements in child functioning. These findings would support the assertion that focus on family dynamics in substance abuse treatment programs is an effective use of resources and an important target of intervention efforts.